1. Field of the Invention
The present invention relates to the field of lighter-than-air type craft and, more particularly, to an autonomous stratospheric airship having a neutrally buoyant structure at flight altitude, making use of regenerative electric energy storage and collection. This application claims the benefit of U.S. Provisional Patent Application No. 60/111,835, filed on Dec. 11, 1998.
2. Description of the Related Art
In the past, there have been designed and used a series of dirigibles, other types of lighter-than-air vehicles, hot-air balloons, and so forth, for passenger transport, rescue work, lift capabilities, and transport of goods and supplies. The present invention relates to a powered airship having a buoyant structure designed specifically for operations in the stratosphere. It incorporates an autonomous navigation capability and a regenerative solar electric energy collection and storage system, enabling the airship to remain aloft for extended periods of time, while following a specified course and gathering mission-specific data.
The prior art reveals several attempts at providing a portion of the capabilities embodied in the present invention, but none was found to incorporate all of the capabilities mentioned below and each such attempt tends to utilize rather complicated mechanical structures. U.S. Pat. Nos. 5,333,817 and 5,538,203 both disclose a buoyancy adjustment system for a lighter-than-air vehicle, involving a series of ballonets, each arranged along the longitudinal axis of the airship in equal numbers. The object of these inventions is to provide a system of independent control for ballonet inflation/deflation which dispenses with ducted coupling to the individual ballonets. In addition, U. S. Pat. No. 5,538,203 provides rapid deflation of the same ballonet system, instead of merely venting it to the atmosphere. In either case, this system is rather primitive and does not take into account the differential pressure between the atmosphere, the surrounding airship gas bag, and the pressure within individual ballonets.
U.S. Pat. No. 5,348,254, issued to Nakada, claims an airship design for flights of long duration powered by solar cell batteries and a hydrogen generation system. This system obviates the need for batteries by electrolytic generation of hydrogen; however, accidental puncture of the hydrogen storage envelope can easily result in complete destruction of the airship.
U.S. Pat. No. 4,995,572, issued to Piasecki, describes a multi-stage, high-altitude data acquisition platform comprising the combination of a low-altitude dirigible and a stratospheric balloon for use at 60,000 ft. and above. The primary object of this invention is to provide a stable launch platform for lifting heavy payloads to stratospheric altitudes. The airship contains a silo used to retain the stratospheric balloon for launch from low altitudes. Such a multi-vehicle payload lifting system is rather complex and unnecessary for accomplishing the advantages and objectives of the present invention.
U.S. Pat. No. 4,204,656 issued to Seward III, discloses a bi-axial propulsing control system for airships. This system, as illustrated in the patent drawings, does not distribute the propulsion motor loading equally among the ascent/descent and left/right movement axes. In addition, the torquing forces of the propulsion motor are applied at the ends of the orientation axes, causing greatly increased loading on the propulsion direction drive system.
French Patent No. 86 02734 discloses a dual-axis, symmetric propulsion system for airships. This system comprises a set of two or more motors which move in concert to direct the motion of the airship. This application requires a plurality of motors, unnecessary to implementation of the present invention.
U.S. Pat. No. 4,934,631, issued to Birbas, describes a lighter-than-air vehicle comprising a framework surrounded by a series of inflatable lift bags. Each bag contains a heating element and lifting gas. The propulsion system comprises a shrouded propeller with vanes to direct the propulsive force. While this airship makes use of a single propulsion unit to navigate through the air, it entails a complicated assembly structure which is impractical for inexpensive construction. In addition, the airship has no means of autonomous navigation or maintaining station above a fixed point of the surface of the earth in autonomous fashion.
Japanese Patent No. 5-221387A discloses an airship constructed of transparent materials wherein a solar array is disposed to receive energy from the sun. However, this design is not constructed for multiple-axis array adjustment to capture the maximum amount of solar energy based on the airship position in relation to the sun. Only a single, longitudinal, axis of rotation for the array is shown. Other patents, such as Japanese Patent No. 54-35994, U.S. Pat. No. 5,518,205 issued to Wurst et al., and U.S. Pat. No. 4,364,532 issued to Stark, all describe solar-powered airships with solar cells disposed on the surface structure of the ship. Again, the inherent disposition of the cell structure precludes the use of optimal positioning of the cells to capture the maximum amount of solar energy to be gained given a varied position of the airship in relation to the sun.
None of the aforementioned inventions are directed toward an autonomous platform specifically designed for flight in the lower stratosphere. In addition, none are directed toward an airship which is capable of controlling operational altitude, including maintenance of a fixed position over a point on the surface of the earth, or navigation between predetermined waypoints. Further, none of the prior art is directed toward an autonomous airship having a specially constructed solar array energy extraction source which provides sufficient energy for power during the day, and stores sufficient energy for continuous night-time operation.
Therefore, it is desirable to have an autonomous airship specifically designed for flight in the lower stratosphere, with the ability to maintain a fixed position over a point on the surface of the earth, or navigate between predetermined waypoints. Additionally, it is desirable to have an autonomous airship capable of controlling its operational altitude, using ballonets to control the pitch axis attitude. Furthermore, it is desirable to have an autonomous airship which uses a single motor for propulsion that evenly distributes the propulsive forces along the directive axes of the articulating means. It is also desirable to have an autonomous airship which can utilize solar energy to power propulsion during the day and additionally, store sufficient energy for continuous operation throughout the night.
In accordance with one aspect of the present invention, an autonomous airship designed specifically for flight in the lower stratosphere with the capability for maintaining a fixed position over a point on the surface of the earth is disclosed. Additionally, the airship provides autonomous control and navigation between predetermined waypoints, or may be programmed to remain within the optical line of sight of a predetermined position on the surface of the earth by matching the speed of the wind.
Other features of the airship embodying the present invention include construction from high strength, light-weight, polymer-based film materials for strength, and transparent/translucent material for collection of solar energy by internally-mounted solar arrays. The autonomous airship can be launched in an uninflated condition and does not require control or propulsion during ascent. The internally mounted arrays reduce aerodynamic drag, provide a pointing capability for maximum solar energy collection, are cooled by an air duct, and are contained within a separate chamber which permits access to the arrays from the outside of the airship.
The airship embodying the present invention may include a hull defining an enclosed cavity, a lifting gas, a forward ballonet, an aft ballonet, and an equipment bay disposed within the cavity, the bay defining an enclosed chamber, and an overall air management subsystem, at least one solar array, a multiplicity of energy storage units, and an autonomous control system disposed within the bay, the chamber being in fluid communication with the forward and aft ballonets; a propulsion system attached to the hull and in electrical communication with at least one solar array and the energy storage units; and a multiplicity of tail fins attached to the hull. The air management subsystem may further comprise a forward air management subsystem having a blower and an aft air management subsystem, the forward air management subsystem being in fluid communication with the forward ballonet and the bay, and the aft air management subsystem being in fluid communication with the aft ballonet and the bay. The forward air management subsystem may comprise a forward ballonet pressure sensor and the aft air management subsystem may comprise an aft ballonet pressure sensor. The forward and aft air management subsystems may also each comprise a lifting gas release valve, the valves being in fluid communication with the hull.
The propulsion system of the present invention may further comprise a gimbal housing, a motor and transmission assembly, a motor pivot, and a propeller, the housing being fixedly attached to the hull and pivotally mounted to the pivot, the pivot being fixedly attached to the motor and transmission assembly, the assembly being attached to the propeller.
At least one solar array may be aligned with the central axis of the hull, and may be gimballed about respective elevation and azimuth axes of the array. At least one solar array may provide electrical power to the propulsion system during daytime flight operations and the multiplicity of energy storage units may provide electrical power to the propulsion system during night time flight operations.
The autonomous control system of the present invention, the overall air management subsystem, and the propulsion system may provide navigational control between selected waypoints, wherein the autonomous control system may include a GPS receiver and a compass. Therefore, the overall air management subsystem, the autonomous control system, and the propulsion system may be adapted to control movement of the airship about its center of gravity.
The hull of the present invention may have an outer surface and a multiplicity of tail fins may be disposed in a first position contiguous with the outer surface of the hull during ascent to flight altitude and the multiplicity of tail fins may move to a second position non-contiguous with the surface of the hull as the hull inflates due to a reduction in atmospheric pressure.
The present invention may also include, as an alternative embodiment, a hull defining an enclosed cavity; a lifting gas and at least one solar array disposed within the cavity; a forward ballast reservoir; an aft ballast reservoir; a ballast management subsystem attached to the hull and in fluid communication with the forward and aft ballast reservoirs; an equipment bay attached to the hull, the bay having a multiplicity of energy storage units and an autonomous control system; a propulsion system attached to the hull and in electrical communication with at least one solar array and the energy storage units; and a multiplicity of tail fins attached to the hull. The ballast management subsystem may further comprise fluid lines between the forward and aft ballast reservoirs, a ballast valve, and a ballast exhaust.
The alternative embodiment airship propulsion system of the present invention may further comprise a gimbal housing, a motor and transmission assembly, a motor pivot, and a propeller, the housing being fixedly attached to the hull and pivotally mounted to a pivot, the pivot being fixedly attached to a motor and transmission assembly, the assembly being attached to the propeller.
In this alternative embodiment at least one solar array may be aligned with a central axis of the hull, and the array may be gimballed about respective elevation and azimuth axes of the array. At least one solar array may provide electrical power to the propulsion system during daytime flight operations and the multiplicity of energy storage units may provide electrical power to the propulsion system during night time flight operations.
The autonomous control system, the ballast management subsystem, and the propulsion system in this alternative embodiment of the present invention may provide navigational control between selected waypoints, wherein the autonomous control system may include a GPS receiver and a compass. Therefore, the ballast management subsystem, the autonomous control system, and the propulsion system may be adapted to control movement of the airship about its pitch and yaw axes.
The hull in the alternative embodiment of the present invention may have an outer surface and a multiplicity of tail fins may be disposed contiguous with the outer surface of the hull during ascent to flight altitude, wherein the multiplicity of tail fins may move to a second position non-contiguous with the surface of the hull as the hull inflates due to a reduction in atmospheric pressure.